The present invention generally relates to measuring semiconductor wafers being an intermediate product in the fabrication of integrated circuits (ICs), and, more particularly, relates to an apparatus and to a method for supporting wafers during measurement.
In semiconductor manufacturing, structures are obtained on semiconductor wafers or substrates to form a variety of electronic components on the wafer, such as transistors. The wafers are processed, for example, by well-known lithography and etching steps in chambers. Due to variations in the process steps, the frontside of the wafers are continually monitored to determine if the dimensions of the structures (e.g., width and depth of a trench) are within acceptable range. Such monitoring, generally referred to as xe2x80x9cmetrologyxe2x80x9d is performed by well-known metrology tools that comprise, for example, scanning electron microscopes (SEM), optical measurement devices, laser interferometers, atomic force microscopy (AFM) devices, or the like. The structure dimensions can also be investigated by probe tools.
Metrology tools provide information on critical processing features (such as pattern critical dimensions on the wafer) during manufacturing. Probe tools give information on the performance of the component (such as speed and functionality) after manufacturing is completed (or nearly completed).
Both for metrology tools and for probe tools, the distance (Z direction) between tool and wafer is of major importance and should be maintained substantially constant for all XY coordinates of the wafer. During measuring, the wafer is supported by a chuck that allows fine displacement of the Z direction.
However, chucks are susceptible to wafer backside contamination resulting in a substantial non-uniformity of the distance between the frontside of the wafer and the metrology tool. This is not desired.
The present invention seeks to provide an improved chuck as well as a method that mitigate or avoid disadvantages and limitations of the prior art.